Among conventional methods hitherto known for detecting torque and rotation angle, one method is disclosed, for example, in Japanese Unexamined Patent Publication, No. H11-194007. FIG. 13 shows the method of detection disclosed therein.
In a torque detector of FIG. 13, gears 126a and 126b are mounted in a manner to make engagement via linkage springs 127a and 127b to their respective shafts (not show in the figure) of which a rotation angle is to be detected.
These gears 126a and 126b engage with gears 129a and 129b respectively. Gears 129a and 129b bear coded disks 128a and 128b mounted respectively thereto, each of which is provided with a plurality of magnetic poles on a periphery thereof. The magnetic poles provided around coded disks 128a and 128b move with rotation of the shafts, of which a rotation angle is to be detected. Detector elements 130 and 131 are mounted in positions, each facing the periphery of respective one of coded disks 128a and 128b, and they count a number of the magnetic poles traveling over them for detection of a rotation angle of the shafts.
A mechanism of the above structure is mounted in engagement with two shafts which are connected to each other through a torsion bar. In this case, the torque detector detects an amount of torque acting between the two shafts by comparing two rotation angles detected individually on the shafts, when the torque produces a twist between them.
In the torque detector constructed as above, detector elements 130 and 131 disposed in positions lateral to the shafts detect magnetic fields generated by the magnetic poles on the peripheries of coded disks 128a and 128b. Therefore, for example, it is liable to variation in detecting accuracy due to changes in spaces between coded disks 128a and 128b and detector elements 130 and 131 in relation to gears 126a and 126b, if any of gears 129a and 129b and coded disks 128a and 128b receives an external force in a direction orthogonal to their axes during the assembling process.
Furthermore, this torque detector of the prior art uses the magnetic fields generated by the magnetic poles of coded disks 128a and 128b for detection by detector elements 130 and 131. Therefore, it has a limitation in resolution of the detection which is determined by a dimension of intervals of the magnetic poles, and it is hence difficult to detect with high resolution a small movement of the steering wheel, an amount of torque, a rotation angle and a rotational speed at the initial state when the wheel begins being turned.